Anamorphic objective lens

ABSTRACT

An anamorphic objective lens comprising, along an optical axis and in order from an object space to an image space: at least a negative (−) spherical first lens group; an anamorphic second lens group and a positive (+) spherical third lens group wherein an aperture stop is located before, after or preferably within the spherical third lens group. Both spherical lens groups contain spherical refractive optical surfaces and the anamorphic lens group contains cylindrical and plano optical surfaces with at least one cylindrical surface oriented at substantially 90 degrees about at least one other cylindrical surface. The negative spherical first lens group may provide focusing.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 37 CFR §119(e) of U.S.Provisional Application No. 61/808,343 filed Apr. 4, 2013, the contentsof which are incorporated herein their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO A “SEQUENCE LISTING”, A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON COMPACT DISC

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to anamorphic objective lenses, and moreparticularly to a range of different focal length anamorphic objectivelenses providing traditional anamorphic imaging characteristics andhaving relatively simple optical surface shapes and correspondingpotential minimized cost by having an arrangement of three lens groupswith spherical, anamorphic and spherical powers and an optical stoplocated outside of the first and second lens groups.

2. Description of Prior Art Including Information Disclosed Under 37 CFR1.97 and 1.98

Contemporary anamorphic objective lenses normally have an optical axisand are commonly based on a front anamorphic lens group havingpredominantly X cylinder refractive optical surfaces and a rearspherical lens group with an optical stop in the rear spherical lensgroup or between the rear spherical lens group and the front anamorphiclens group that may be in the form of a variable aperture diameter irisor diaphragm.

This anamorphic objective lens arrangement produces images havingnumerous residual optical aberrations and characteristics most of whichare desired by cinematographers because they produce an artistic lookthat is different from spherical objective lenses.

Many of the less desired residual optical aberrations andcharacteristics of this arrangement were accepted by cinematographerswith film based cameras but with the advent and adoption of electronicsensor based digital cameras some of them have become less acceptable.In particular the amount of residual chromatic aberration has becomeless tolerable whereas some field curvature combined with some residualastigmatism is still acceptable.

Specific anamorphic objective lens characteristics of this arrangementsuch as the oval or elliptically shaped of out of focus objects commonlyreferred to as the bokeh as compared to the spherical shape produce byspherical objective lenses is preferred because of the distinctiveartistic look produced. Another characteristic that is desired becauseof the distinctive artistic look produced is the depth of field beingdifferent in the vertical azimuth direction of the field versus thehorizontal azimuth direction of the field. In the case of an anamorphicobjective lens that squeezes the horizontal field of view bysubstantially two times as compared to the vertical field of view, thedepth of field in the horizontal azimuth direction of the field issubstantially two times greater than the depth of field in the verticalazimuth direction of the field.

Improving the optical aberrations and characteristics of anamorphicobjective lenses of this arrangement may involve increasing opticalsurface shape complexity and hence manufacturing cost including addingaspherical and free-form shaped optical surfaces.

Thus, to address the artistic need of cinematographers and maximize theimaging potential of both film and digital cameras a cost effectiveanamorphic objective lens arrangement with a suitable blend of residualoptical aberration correction and characteristics needs to be achieved.

BRIEF SUMMARY OF THE INVENTION

An anamorphic objective lens comprising along an optical axis and inorder from an object space to an image space at least a negative (−)power spherical first lens group, an anamorphic second lens group, apositive (+) power spherical third lens group and having an optical stoplocated before or after or preferably within the spherical third lensgroup. The anamorphic second lens group has at least one cylindricalsurface in a first direction and at least a second cylindrical surfacein a substantially perpendicular direction to the first direction toenable a high degree of aberration correction over the whole image,whereby the residual longitudinal chromatic aberration and the residuallateral chromatic aberration are substantially reduced. The negativelypowered spherical first spherical lens group may provide focusing bymovement of at least one of the lens elements contained therein and mayexhibit low breathing in the focus range.

The anamorphic second lens group provides a squeeze of the field of viewso that the focal lengths in the X and Y directions are different by aratio of about two times which is typical for traditional anamorphicoptical systems. The positively powered third lens group adjacent theimage space delivers the radiation passing through the optical system onto the image sensor with nearly telecentric light paths and suitablyhigh relative illumination, thereby increasing the efficiency of manyelectronic sensors.

In accordance with one aspect of the present invention, an anamorphicobjective lens is provided including, along an optical axis and in orderfrom an object space to an image space, a negative (−) spherical powerfirst lens group; an anamorphic second lens group, a positive (+)spherical power third lens group, and an aperture stop. The aperturestop is located in a position either before, after and within thespherical power third lens group.

Preferably, the aperture stop is located within said positive (+)spherical power third lens group.

The negative (−) spherical first lens group is configured to providefocusing.

In accordance with another aspect of the present invention, ananamorphic objective lens is provided including a first lens group withspherical powers of a first type, a second lens group with sphericalpowers of a second type, a third lens group with anamorphic powers, andan optical stop. The third lens group is interposed between the firstlens group and the second lens group. The optical stop is locatedoutside the first lens group and the third lens group.

The spherical powers of the first type are opposite to the sphericalpowers of the second type. The spherical powers of one of the first typeand the second type are negative spherical power. The spherical powersof the other of the first type and the second type are positivespherical powers.

The anamorphic objective lens has an optical axis. The first, second andthird lens groups are situated along said optical axis. The anamorphicobjective lens is adapted for use between an object space and an imagespace. The optical axis extends between the object space and the imagespace.

The anamorphic second lens group has at least one cylindrical surface ina first direction and at least one cylindrical surface in a directionsubstantially perpendicular to said first direction.

The anamorphic second lens group has focal lengths in the X and Ydirections which differ and together with the other lens group focallengths altogether produce focal lengths in X and Y directions whichdiffer by a ratio of about two times.

The anamorphic objective lens preferably has a focal length within therange of from 25 mm to 135 mm in the Y direction.

The anamorphic objective lens provides low residual chromaticaberration, a traditional oval bokeh shape, and different depths offield in the vertical and horizontal azimuth directions of the field.

The anamorphic objective lens has a medium fast full aperture moderatelywide angle field of view of the fixed focal length (prime) type.

The lens groups of the anamorphic objective lens are fabricated of lenselements made of glass.

The lens groups with spherical powers include a lens element with arotationally symmetrical surface shape about the optical axis.

The lens group with anamorphic powers includes a lens element with anon-rotationally symmetrical surface about the optical axis.

The anamorphic objective lens preferably operates at an aperture off/2.4 and over a waveband of 455-656 nm.

The anamorphic second lens group comprises five cylindrically surfacedlens elements with four Y cylinders, three X cylinders and three planosurface shapes.

The spherical first lens group includes two lens elements, one of whichis axially moveable relative to the other.

The spherical third lens group includes seven lens elements.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF DRAWINGS

To these and to such other objects that may hereinafter appear, thepresent invention relates to an anamorphic lens as described in detailin the following specification and recited in the annexed claims, takentogether with the accompanying drawings, in which like numerals refer tolike parts and in which:

FIG. 1 is a lens plot in the YZ elevation (side view) on an optical axisØ where the Y direction focal length is 42.47 mm with three fields shownat zero, top and bottom of the field of view and the top to bottomdiagrams showing far, intermediate and close focus distancearrangements.

FIG. 2 is a lens plot in the XZ elevation (plan view) on an optical axisØ where the X direction focal length is 21.47 mm with three fields shownat zero, top and bottom of the field of view and the top to bottomdiagrams showing far, intermediate and close focus distancearrangements.

FIG. 3 is an image plot for the image points used in the transverse rayaberration and MTF plots in FIGS. 4-15.

FIG. 4-9 are transverse ray aberration plots at far, intermediate andclose focus distances with five fields shown in each Figure and 10fields spread across the image for each focus distance.

FIG. 10-15 are MTF plots at far, intermediate and close focus distanceswith five fields shown in each Figure and 10 fields spread across theimage for each focus distance.

FIG. 16 is a field plot of the field of view covered at far,intermediate and close focus distances.

The information shown in FIGS. 1-16 was generated by CodeV® opticaldesign software, which is commercially available from Synopsis OpticalResearch Associates, Inc., Pasadena, Calif., USA.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to anamorphic objective lenses, and in particularto a range of different focal length anamorphic objective lensescovering at least a focal length range from 25 mm to 135 mm andproviding low residual chromatic aberration, a traditional oval bokehshape and different depths of field in the vertical and horizontalazimuth directions of the field.

The term “lens group” as used in connection with the anamorphicobjective lens disclosed herein means one or more individual lenselements. Also, the terms “optical stop” and “stop” are equivalent termsthat can be used interchangeably. A “field stop” as the term is usedherein is a stop where the chief rays do not go through the center ofthe stop at the optical axis and the general purpose of a field stop isto vignette the edges of the radiation beams.

In the example provided herein, the front lens group is negativelypowered and the rear lens group is positively powered and they have beenpaired with an anamorphic lens group to work in unison and match thepreferred optical interface characteristics of sensors, where neartelecentric radiation beams approach the sensor.

The example embodiment discussed below is a medium fast full aperturemoderately wide angle field of view anamorphic objective lens of thefixed focal length (prime) type.

In the example embodiment, all of the lens elements are made fromglasses. The lens element optical surface shapes in the spherical firstlens group and the spherical third lens groups are all rotationallysymmetrical about the optical axis such as spherical and in theanamorphic second lens group at least one lens element surface shape isnon-rotationally symmetrical about the optical axis such as cylindrical.

The aforementioned optical example, although providing these kinds offeatures and others like low breathing and telecentric radiation outputat the sensor, are capable of achieving suitable levels of variousperformance including image quality resolution and contrast, highrelative illumination for low shading and efficient optical throughputat the sensor via near telecentric radiation output at the sensor, whichtelecentric radiation output is less than about 10 degrees.

The novel configuration of having a negatively powered spherical firstlens group, an anamorphic second lens group followed by a positivelypowered spherical third lens group containing an optical stop mayproduce some residual distortion, astigmatism and field curvatureaberrations but those aberrations to a tolerable extent contribute tothe anamorphic look as desired by many cinematographers. In addition, abalanced blend of the afore-described lens characteristics may aid incost reduction of manufacture. With the advent and adoption of digitalcameras employing electronic sensors a large back focal length which wasonce required for film cameras having a reflex mirror may be lessnecessary but is still provided for in the novel anamorphic objectivelens.

The example embodiment disclosed operates at an aperture of f/2.4 andover a waveband of 455-656 nm and this waveband is what was used in theTransverse Ray Aberration (TRA) Figures (see bottom right of TRAFigures) and in the MTF Figures (see top right of MTF Figures). A fasteror slower aperture may be required and an extended waveband may berequired. The aperture may be increased or reduced and the wavebandexpanded and the optical designs re-optimized to maximize image qualityover such apertures and wavebands without departing from the invention.Also, during such re-optimization alternate glass types may be usedwithout departing from the spirit and scope of the disclosure.Furthermore, more complex optical surface shapes such as aspherical andfree-form surfaces may be introduced for expanded performance but at thelikely effect of increased manufacturing cost.

FIGS. 1-16 relate to an example embodiment in which the focal length inthe Y and X directions are 42.47 mm and 21.47 mm, the overall length is245 mm from the first refractive surface vertex of the lens to the imagevertex, the front diameter clear aperture is 89.61 mm, the back focallength from the rear refractive surface vertex to the image vertex is36.07 mm and the close focus distance from the object to the image is985.00 mm. The focal lengths of the spherical first lens group,anamorphic second lens group and spherical third lens group are 130.62mm, −132.23 mm and 133.86 mm for the far, intermediate and close focusdistances, 1032.81 mm in the Y direction and −140.60 mm in the Xdirection and 66.75 mm.

The focal lengths of the five lens elements of the anamorphic secondlens group containing at least one cylindrical surface are in order froman object space to an image space −81.27 mm (in X direction), −64.50 mm(in X direction), 1379.50 mm (in Y direction), 90.87 mm (in X direction)and 6151.28 mm (in Y direction. It is to be understood that the focallengths of the five lens elements of the anamorphic second lens group inthe other X and Y directions are substantially large and hence havelittle optical power. The nominal image size is 8.91 mm vertical halfheight and 10.65 mm horizontal half width.

The lens system comprises a total of fourteen lens elements with twelvesinglets and one doublet. The spherical first group contains two lenselements with one element axially movable for focusing at differentdistances, the anamorphic second lens group contains five cylindricallysurfaced lens elements with four Y cylinders, three X cylinders and 3plano surface shapes and the spherical third lens group contains sevenlens elements. The optical stop lies within the spherical third lensgroup. In this example embodiment the telecentric radiation output isabout 7.8 degrees at all three focus positions.

Optical prescription Table 1 is set forth below in the Appendix anddescribes a select example of the embodiment of the anamorphic objectivelens disclosed herein.

Table 2 contains focal length, anamorphic squeeze and illumination data.In Table 2 it is shown that the relative illumination is above 40%,which is sufficiently high for low shading across the field of view whenan anamorphic objective lens is used in combination with an electronicsensor at the image plane, such as when the anamorphic objective lensconstitutes part of a digital camera.

In FIGS. 4-9, the transverse ray aberration performance for the exampleembodiment is shown with minimized residual astigmatic and longitudinaland lateral chromatic aberrations on curved image surfaces toapproximately emulate curved object surfaces. FIGS. 4 and 5 showtransverse ray aberration plots at a far focus distance, 6 and 7 showtransverse ray aberration plots at an intermediate focus distance andFIGS. 8 and 9 show transverse ray aberration plots at a close focusdistance.

In FIGS. 10-15, the polychromatic MTF performance at a spatial frequencyof 20 cycles/mm is shown for the example embodiment to be greater than70% at all field positions at the far and close focus distances andgreater than 75% for all axial field positions at an intermediate focusdistance. FIGS. 10 and 11 show MTF at a far focus distance, FIGS. 12 and13 show MTF at an intermediate focus distance and FIGS. 14 and 15 showMTF at a close focus distance.

In FIG. 16, the periphery of the field of view at far, intermediate andclose focus distances is shown on a plane in object space located atsubstantially 3.66 m from the image surface. The variation in the fieldof view size is mainly dependent on variations through focus in theanamorphic squeeze ratio, distortion in X and Y directions and focusbreathing caused by change in the X and Y focal lengths.

Field stops may be employed in additional locations to those given inTable 1 for the example embodiment. They may be located anywhere withinthe lens system. Their purpose is to vignette the radiation and may becircular or rectangular or even rectangular with radius corners.

The five lens elements in the anamorphic second lens group with thecylindrical surfaces of the example embodiment additionally may eachhave two refractive surfaces which may be formed by X and Y cylindricalsurfaces or Y and X cylindrical surfaces with the X and Y surfacessubstantially perpendicular to one another. This arrangement may improvethe imaging characteristics but likely at the effect of additionalmanufacturing cost.

Although the present invention has been fully described in connectionwith an embodiment thereof with reference to the accompanying drawingsand data listing, it is to be noted that various changes andmodifications including smaller and larger focal lengths, smaller andlarger anamorphic squeeze ratios, smaller and larger full aperturef/numbers, smaller and larger image sizes, smaller and larger wavebands,etc. (e.g., 435 nm to 656 nm) may be made as will be apparent to thoseskilled in the art. Such changes and modifications are to be understoodas being included within the scope of the present invention as definedby the appended claims.

What is claimed is:
 1. An anamorphic objective lens comprising along anoptical axis and in order from an object space to an image space: anegative (−) spherical power first lens group; an anamorphic second lensgroup comprising at least one lens element having a non-rotationallysymmetric surface shape about the optical axis; a positive (+) sphericalpower third lens group, and an aperture stop; wherein all lens elementshaving a non-rotationally symmetric surface shape about the optical axisare located between the object space and the aperture stop such that theanamorphic objective lens creates a traditional oval or elliptical bokehof out of focus objects.
 2. The anamorphic objective lens of claim 1wherein said aperture stop is located before, after or within saidpositive (+) spherical power third lens group.
 3. The anamorphicobjective lens of claim 1, wherein said negative (−) power sphericalfirst lens group is configured to provide focusing.
 4. The anamorphicobjective lens of claim 1 wherein said anamorphic second lens group hasat least one cylindrical surface in a first direction and at least onecylindrical surface in a direction substantially perpendicular to saidfirst direction.
 5. An anamorphic objective lens comprising along anoptical axis and in order from an object space to an image space: anegative (−) spherical power first lens group; an anamorphic second lensgroup; a positive (+) spherical power third lens group, and an aperturestop; wherein only said anamorphic second lens group includes a lenselement having a non-rotationally symmetric surface shape such that theanamorphic objective lens creates a traditional oval or elliptical bokehof out of focus objects.
 6. The anamorphic objective lens of claim 5wherein said anamorphic second lens group comprises at least one lenselement having a cylindrical surface in a first direction and at leastone lens element having a cylindrical surface is a directionsubstantially perpendicular to said first direction.
 7. The anamorphicobjective lens of claim 1 or 5 wherein said anamorphic second lens grouphas focal lengths in the X and Y directions which differ by a ratio ofabout two times.
 8. The anamorphic objective lens of claim 1 or 5 havinga focal length within the range of from 25 mm to 135 mm.
 9. Theanamorphic objective lens of claim 1 or 5, wherein the anamorphicobjective lens creates low residual chromatic aberration.
 10. Theanamorphic objective lens of claim 1 or 5 wherein the anamorphicobjective lens creates different depths of field in the vertical andhorizontal azimuth directions of the field.
 11. The anamorphic objectivelens of claim 1 or 5 wherein said lens creates a medium fast fullaperture moderately wide angle field.
 12. The anamorphic objective lensof claim 1 or 5 wherein said lens groups are fabricated of lens elementsmade of glass.
 13. The anamorphic objective lens of claim 1 or 5 whichoperates at an aperture of f/2.4 and over a waveband of 455-656 nm. 14.The anamorphic objective lens of claim 1 or 5 wherein said anamorphicsecond lens group comprises five cylindrically surfaced lens elementswith four Y cylinders, three X cylinders and three plano surface shapes.15. The anamorphic objective lens of claim 1 or 5 wherein said sphericalpower first lens group comprises two lens elements, one of which isaxially moveable relative to the other.
 16. The anamorphic objectivelens of claim 1 or 5 wherein said spherical power third lens groupcomprises seven lens elements.
 17. The anamorphic objective lens ofclaim 1 or 5 wherein at least one vignetting field stop aperture islocated before said optical stop.
 18. The anamorphic objective lens ofclaim 1 or 5 wherein at least one vignetting field stop aperture islocated after said optical stop.
 19. The anamorphic objective lens ofclaim 1 or 5 wherein at least one vignetting field stop aperture islocated before and after said optical stop.